The operation of internal combustion engines in the presence of unfavorable operating conditions can lead to the formation of deposits in the combustion chamber. Especially for engines having direct fuel injection, deposits can form, for example, on the injection valves, that is, on the tips or in the tips of the injection valves. These deposits can operate unfavorably on the spray preparation and therefore on the combustion. As a rule, one speaks of a coking of the injection valves.
An electronic control arrangement is known from DE 198 28 279 A1 by means of which an equalization of the cylinder-individual torque contributions can be carried out in a multi-cylinder engine. Here, to balance the cylinder-individual torque contributions, the injected fuel quantity, the ignition time point (for a spark-ignition engine), the exhaust gas recirculation rate or the injection position are varied. The determination of the cylinder-individual torque contributions can take place via the evaluation of the time-dependent trace of the rotational movement of the crankshaft or camshaft and wherein individual segment times are detected. Alternatively, rough running values can be used which are anyway formed in the control apparatus for the detection of combustion misfires. The aim of the cylinder equalization is to minimize the rough running values with a control concept. Corresponding interventions can be undertaken on the engine in dependence upon the detected pattern and from the magnitude of the individual filtered and unfiltered rough running values. A coking of injection valves can cause a torque of the corresponding cylinder which is too low especially in an engine having direct injection. In this case, the corresponding cylinder runs too lean. The main components for the control function are cylinder-individual PI controllers in correspondence to DE 198 28 279 A1.
U.S. patent application publication 2003/0159677 describes a method and an arrangement for monitoring the effects of a cylinder equalization control. Corresponding to the introduction of the description, it is a special requirement for a direct-injecting spark-ignition engine. Here, an increased rough running can occur caused by a low tolerance compatibility of the combustion process in stratified operation and/or because of tolerances of the high pressure injection valves which are used or in the distribution of the fuel to the individual cylinders. Also, deterioration-caused changes of the throughflow characteristics of the high pressure injection valves can have an effect. In the context of U.S. patent application publication 2003/0159677, preferably the torque contribution (actual torque) of a cylinder relative to its ignition predecessor is detected (that is, no absolute torque determination) via an evaluation of the time-dependent trace of the crankshaft rotation or camshaft rotation. Improvements in the area of cylinder equalization are achieved in that a monitoring of the effects for the cylinder equalization control is provided and in that a corresponding fault signal is generated for disturbances in the area of the cylinder equalization control. The monitoring of the effects takes place in such a manner that the cylinder-individual torque contributions can be checked after a completed cylinder equalization control intervention to determine if the control shows an effect. If the effect does not occur to the extent as wanted, the control loop amplification of the cylinder-individual PI controllers is successively reduced to a pregiven end value. The control thereby functions with greater robustness but is dynamically slower which is accepted. If the wanted effect does not occur after adjusting the PI controllers to the pregiven end value, then a fault signal is generated.
The disclosure of the last-mentioned U.S. patent application publication 2003/0159677 is expressly incorporated into this application.